The present invention relates to an FED and, more particularly, to an electrode arrangement on the rear substrate.
As shown in FIG. 7 a conventional FED is comprised of two spaced apart substrates on one of which are formed a plurality of pairs of electrodes 3,5 with electron emitters between them. One electrode 3 serves as scanning electrode while the other electrode as data electrode. On undersurface of the second substrate 9 facing the first substrate 1 are formed transparent anode electrodes 11 and a phosphor layer 13 on top of them. When a predetermined voltage is applied between the scan electrode and data electrode a portion 7a of the emitter 7 begins to emit electrons which are induced toward the anodes to collide with the phosphor. Here when a pulse width modulated (PWM) pulse is used to drive the scan electrodes a negative voltage over a threshold is applied to the scan electrode and a positive voltage corresponding to a desired level of brightness is applied to the data electrode. However, the aforementioned conventional electrode structure has a drawback of deviation of individual devices from the standard during mass production. More specifically the threshold voltage may vary from one device to another. The result is that some may not be able to display a gray scale image and others lower brightness and contrast. Moreover, this conventional structure requires a large amount of current in the data electrodes and thus high power IC drivers making such devices less attractive commercially.
It is an objective of the present invention to provide an electrode structure that is able to prevent low contrast/brightness of a displayed image due to variation of required threshold voltage to cause emission of electrons from the emitters. It is another objective of the present invention to ensure electron emission from a designated portion of electron emitters. The rear substrate of an FED comprises data electrodes formed on a surface of the substrate, an insulating layer over the substrate covering the data electrodes, scan and common electrodes laterally disposed on the insulating layer such that they are parallel with each other and electron emitting elements, which emit electrons when they subject to electric field, connected between a scan electrode and a common electrode. The electron emitting elements have a middle portion narrower than end portions so that electron emitting surface area is located at a same location from emitter to emitter.